we were nearing the ancient city and archaeological site of dmanisi. >> dmanisi is finally in sight andof the most important human migration sites outside of africa. >> sreenivasan: salopek is following the path humans took after the ice age, 70,000 to 100,000 years ago. but here in dmanisi, that path is much older. along these green and jagged river gorges, man has walked-- in one form or another-- for nearly two million years. the history here is stacked high, part of what salopek calls "the layer cake effect" of the caucasus. with a happy dog welcoming us, we passed what was likely an outer defensive tower of the 1,400-year-old city of dmanisi. >> sreenivasan: this has been a crossroads for a long time. >> since day one. pretty much everybody invaded it. >> sreenivasan: was this a trading route? >> this was a silk road trading route city, a big shining city on the hill, very rich until the mongols came and plundered it. and they were here a few hundred years until the georgians and armenians pushed them out. >> sreenivasan: it's an archeological goldmine. with the summer digging seas

dmanisi, in particular, is 1.8 million years old. >> woodruff: all that and more on tonight's pbs newshour

: after tea and a bit more conversation, we set out for the next waypoint: the ancient village of dmanisi we'll tell you about in our next story - about six miles away. but as we soon found out, even the most-precise directions need updating, which we were given by a man with hands stained from a life time of gathering walnuts. and that, says salopek, is just part of the plan. you've got g.p.s., you've got maps, you've got guides, you are still going the wrong way sometimes. >> being found is overrated. being a little lost is good because it keeps you alert, keeps you looking around. it keeps you scanning the horizons about to find your bearings and you are not sleepwalking through the world. >> sreenivasan: so how many pairs of shoes do you think you've gone through? >> this is the fourth. somebody brought me these from the states, so they're kind of special. >> sreenivasan: do you get tired by the end of an average day or has your body gotten used to this pace? >> i do. you know, it depends on my physical condition. you know the walk has kind of turned into my life, so it's a complicate